|Número de publicación||US4770526 A|
|Tipo de publicación||Concesión|
|Número de solicitud||US 06/929,623|
|Fecha de publicación||13 Sep 1988|
|Fecha de presentación||12 Nov 1986|
|Fecha de prioridad||13 Nov 1985|
|También publicado como||DE3540157A1, DE3540157C2|
|Número de publicación||06929623, 929623, US 4770526 A, US 4770526A, US-A-4770526, US4770526 A, US4770526A|
|Inventores||Sigmund Manhart, Peter Dyrna, Bernd Kunkel|
|Cesionario original||Messerschmitt-Boelkow-Blohm Gmbh|
|Exportar cita||BiBTeX, EndNote, RefMan|
|Citas de patentes (4), Citada por (60), Clasificaciones (9), Eventos legales (4)|
|Enlaces externos: USPTO, Cesión de USPTO, Espacenet|
The invention relates to a ranging method and apparatus for ascertaining the distance to a target by employing the laser radar impulse transit time principle. A single detector element is used for producing the start signals as well as the stop signals for the time interval measurement or time difference measurement.
Radar ranging devices employ a modulated laser signal for measuring the distance between the ranging device and a target, whereby the transit time of the modulated laser signal from the ranging device to the target and back again is determined. The time difference ΔT between the transmitting of the laser signal and the receipt of the signal reflected by the target is a direct measure for the distance D to be measured according to the following formula ##EQU1## wherein c is the speed of light in vacuum equal to 299793 km/s; and wherein no corresponds to 1.0003 representing the refractive index for the normal atmosphere.
A precise ranging requires a precise time interval measurement. For example, a change in the distance to the target by one millimeter corresponds to a change in the time difference of only 2.7 ps. Therefore, it is generally accepted practice to transform the measured values in order to obtain the required time resolution. In one method the time interval signal to be measured is stretched or lengthened in time by electronic methods. In another method the time interval signal to be measured is transformed into another measured value.
In connection with a ranging system using continuously modulated radiation sources, the phase location of the transmitter signal is compared with the phase location of the receiver signal. The time expansion or stretching is accomplished by mixing the two signals in a local oscillator the frequency of which is slightly shifted relative to the transmitter frequency. The resulting intermediate frequencies of the transmitted signal and of the received signal exhibit the same phase difference as the original frequencies. Thus, a time expansion is accomplished with the aid of the frequency mixing, whereby the ratio of expansion is the ratio of the transmitter frequency to the intermediate frequency.
Another known system employs a single pulse measurement, whereby the time difference is determined in that during the time interval to be measured a capacitor is charged with a constant current. Upon completion of the charging time the charge state of the capacitor may be directly ascertained or measured. One way of ascertaining the charging state is to directly measure the voltage across the capacitor. This method is known as the time-to-amplitude conversion method (TAC). In another method the capacitor is discharged after its loading has been completed, by a constant but substantially smaller current, whereby the discharge time represents a stretching of the charging time to thus represent a stretching of the time interval to be measured. This method is known as the time-to-time conversion method.
All methods which require a precise target ranging use a single detector and preamplifier for the outgoing transmitted signal and for the reflected target signal. The outgoing signal is also referred to as the start signal or the reference signal. The target signal is also referred to as the signal to be measured or as the stop signal. In this type of measurement the electronic delays in the detector and in the preamplifier are the same for both signals. Reference is made in this connection to European patent application (EP-Al) No. 0,057,447 corresponding to U.S. Pat. No. 4,521,107 (Chaborski et al.).
All known methods have several disadvantages. Thus, in connection with the continuous signal modulation a repeated switching is necessary between the two optical measuring ranges, namely the range to the target and the reference range. This repeated switching which may be done either mechanically or electro-optically, adversely influences the reliability and the useful life of the equipment. Besides, a precise phase measurement requires relatively long measuring time durations.
In connection with the pulse ranging method the mechanical or electro-optical switching of the measuring channels is avoided because the reference signal and the target signal appear at the detector at different times. Thus, the switching can be accomplished by strictly electronic means by setting a time gate or several time gates directly in the signal evaluating circuit. The time interval between the reference and target signals may now, as explained above, be measured in different ways, for example, by the time amplitude conversion method or by the time-to-time conversion method.
The accuracy of the time amplitude conversion method is undesirably low because the loading current is not constant, because the capacity of the capacitor depends on the temperature, because there are capacitor leakage currents, and because the comparator response thresholds are not stable.
On the other hand, the precision of the time-to-time conversion method is limited by the inaccuracies of the charging and discharging currents and by the temperature dependency of the switching thresholds. Further, a precise time base such as a quartz clock signal generator is necessary for measuring the stretched time interval. However, quartz oscillators have upper frequency limits so that a quantizing error noticeably affects the digitizing of the measuring interval. It would be advantageous if the clock signal generator frequency could be very high. However, the stabilizing of high frequency oscillators requires a substantial effort and expense for circuitry. Additionally, a continuous calibrating of the frequency of such high frequency standard oscillators is necessary for precise measurements.
In view of the foregoing it is the aim of the invention to achieve the following objects singly or in combination: to provide a method and apparatus for precise ranging which avoid the above mentioned disadvantages of the prior art, more specifically, to provide a higher measuring precision in the described ranging while simultaneously the apparatus is less trouble-prone and less susceptible to interferences while being simpler than prior art ranging devices; to employ a continuous calibration of an optical path of fixed length for avoiding system errors that may be caused by current variations in the time stretching circuit and by instabilities in the time base that is in the clock frequency generator; and to avoid mechanical and electro-optical switching operations altogether and to use only electronic time gates.
The method according to the invention is characterized in that a first proportion or fraction of the laser transmitter signal is passed through a first optical delay path forming a first reference path while simultaneously a second fraction or proportion of the laser transmitter signal is passed through a second optically longer delay path forming a second reference path, whereby both of these delay paths are directly connected to the single receiver detector for providing first and second reference signals, while the remainder of the laser transmitter signal is directed toward the target for producing a reflected or target signal. The time difference between the first reference signal and the target signal is determined as a measure for the range or distance to the target and the time difference between the first reference signal and the second reference signal is used as a calibrating measure. The last step of the present method involves ascertaining the actual range by forming the ratio of the two time intervals. Due to the different lengths of the first and second delay path the respective signals arrive at the receiver detector at different times. Thus, a fixed time interval is provided by the two reference signals at each measuring. This fixed time difference corresponds to the optical length difference of the first and second delay paths. This fixed time interval between the two reference signals passing through the first and second reference signal path corresponds exactly to a calibration length or range. As a result, the invention has the important advantage that it is no longer necessary to provide a precise and stable time base such as a standard frequency oscillator, and that electronic time gates can be used.
In order that the invention may be cleary understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein:
FIG. 1 is a schematic block diagram of the circuit arrangement according to the invention;
FIG. 2 illustrates the signals, as a function of time, produced in the operation of the circuit according to FIG. 1;
FIG. 3 is a block circuit diagram for producing clock signals and time gates for use in the circuit of FIG. 1; and
FIG. 4 illustrates schematically the signal relationship in a practical embodiment according to the invention.
In FIG. 1 the laser generator 10 emits laser impulses in accordance with the clock signal from the clock generator 16. The laser impulses are transmitted through a laser light conductor 11 to a first optical decoupling element 12 capable of deflecting a portion of the laser light and passing the other portion to a further optical decoupling element 13 of the same construction and capable of deflecting a portion of the laser light and passing the remainder to a light delay line 14. The small light proportion deflected in the decoupling element 12 is introduced into a first light delay line 22 constituting a first reference path Ref. 1. The light deflected by the second decoupling element 13 is introduced into a second delay line 23 constituting a second reference path Ref. 2. The first reference path Ref. 1 provides a shorter delay than the second reference path Ref. 2. The first delay line 22 leads to a third optical coupling element 32 which feeds the light through an optical laser light conductor 31 to the receiver detector 30. Similarly, the second delay line 22 leads to a fourth coupling element 33 which also passes the respective signal directly through the light conductor 31 to the receiver detector 30. Elements 32,33 pass a target signal ZS.
The signal emerging from the decoupling device 13 reaches a transmitter optical output member such as a lens 15 through the mentioned delay line 14. The lens 15 directs the laser beam in the direction toward the target not shown, in a focused manner. The target reflects the target signal ZS which is received by a receiver optical device such as a lens 35 which supplies the target signal or reflected signal ZS through the light conductor 31 directly to the detector 30 or through a further delay line 14'.
Thus, for each measurement there are three sequentially appearing signals, namely the first reference signal Ref. 1 through the light conductor or delay line 22, the second reference signal Ref. 2 through the light conductor or delay line 23, and the reflected target signal ZS.
Depending on the length of the delay lines 22, 23, and 14 the target signal ZS appears either between the two reference signals Ref. 1 and Ref. 2 or after the two reference signals. The time interval between the reference signal Ref. 1 and the target signal ZS represents a measure for the range to be measured. The time interval between the two reference signals Ref. 1 and Ref. 2 represents a measure for the optical calibration range provided by line 23.
According to the invention the target range or distance to the target is obtained by forming the ratio of the target interval to the calibration interval. For realizing the measurement, time frame signals are derived from the clock signal generator 16. For this purpose two additional outputs of the clock signal generator 16 are connected to pulse discriminator circuits 41 and 42 which also receive at their further inputs the output signal of the receiver detector 30. The time frame signals activate the discriminators 41 and 42. The arrangement is such that the discriminator 41 always responds to the first reference signals Ref. 1 while the discriminator 42 responds alternately to the target signal ZS and to the second reference signal Ref. 2.
Referring further to FIG. 1, the outputs of the two discriminators 41 and 42 are connected to a multi-vibrator 43 for producing a time signal that alternately corresponds to the measured range and to the internal calibration range. The output signals from the multi-vibrator 43 are supplied to a signal stretching circuit 44 which stretches the signal from the target. The output of the signal stretching circuit 44 is supplied to a counter 45 which, under the control of a high frequency oscillator, counts the pulses from the circuit 44. The counter 45 stores the resulting count.
Referring to FIG. 2, the last row shows counted pulses nZ representing the time needed for the light to travel from the transmitter optical output 15 to the target and back again. The pulse count nR represents a reference measurement for the calibration. The respective ranges or distances are calculated as follows. ##EQU2## DZ is the relative distance to the target; DR is the length of the reference or calibration path;
c is the speed of light;
n is the refractive index;
nZ is the target pulse count;
nR is the calibration pulse count;
fo is the pulse frequency of the oscillator 46; and
K is a time stretching factor in the range of 10 to 1000.
The absolute range D to the target is then calculated by dividing the digital pulse count nZ by the digital reference pulse count nR and then multiplying the ratio with the value of the optical calibration path Do. ##EQU3## The foregoing shows that the invention employs a continuous calibration with reference to a fixed optical path. This feature of the invention makes sure that the systematic errors that are unavoidably caused in the prior art due to current variations in the time stretching circuit and due to instabilities in the reference time base, cannot affect the results calculated according to the invention.
According to the invention the time frame switching for the discriminator 42 is accomplished electronically so that any mechanical or electro-optical switching means are avoided. The discriminators 41 and 42 may be constructed as threshold level discriminators in a simple embodiment in which high signal levels are available. Other examples for the discriminators 41 and 42 may comprise so-called zero crossing discriminators or constant fraction discriminators.
The following is a numerical example of the invention.
______________________________________Laser pulse repetition rate 10 kHzLaser pulse width 1 nsDelay line 22 L.sub.22 = 1 m light conductor refractive index (n = 1.5)Delay line 23 L.sub.23 = 49 m light conductor refractive index (n = 1.5)Optical calibration range L.sub.0 = 36 mDelay line 14 L.sub.14 = 5 m light conductor refractive index (n = 1.5)______________________________________
For these figures we obtain a pulse arrangement as shown in FIG. 4, whereby range measurements from 0 to 30 m between the measuring apparatus and the target can be measured, and whereby the fixed time interval reference Ref. 1-Ref. 2 provides a calibration range having a length of 36 m.
Where a pulse or time stretching circuit 44 is used having a time stretching factor K=300, whereby the capacitor loading current is 3 milliamperes and the discharging current is 10 microamperes, and if an oscillator 46 is used having a frequency fo =500 MHz, then the accuracy of the calculation of the individual measurements is as follows ##EQU4## Due to the statistical variations in the pulse discriminators 41 and 42 as well as in the bi-stable multi-vibrator 43 and in the time stretch circuit 44, the stability of the individual measurement is limited to about 30 ps having regard to presently available circuit components. Thus, any individual measurement is in reality not better than 5 mm. However, the systematic errors as just mentioned are eliminated to a substantial extent by the invention as described above. Therefore, it is possible to reduce the statistical errors by the formation of a mean value, for example based on one hundred measurements so that after a measuring time of, for example, 10 ms a certain measured value can be obtained having a precision in the range of 1 mm.
When the apparatus according to the invention is used for measuring larger distances, the delay line 23 may be provided with an optical switch for switching off the reference signal Ref. 2 for measuring the time difference between the reference signal Ref. 1 and the target signal ZS in a conventional way. For increasing the measuring accuracy in this context it is possible to use a quartz controlled oscillator 46.
However, the method according to the invention can also be used for measuring large distances. In this connection it is advantageous to make the delay line 14 longer than the delay lines 22 and 23. Thus, the reference signals Ref. 1 and Ref. 2 appear in time prior to the target signal ZS at the detector 30, even if the target range is 0. Instead of delay line 14, a delay line 14' may be used.
FIG. 3 shows a block diagram of an example embodiment of a circuit arrangement for the time frame generator driven by the clock signal generator 16 to provide the required signals for the discriminator circuits 41 and 42. A first monoflop circuit MF1 is connected with its input to the clock signal generator 16 and provides at its output a pulse train Tn which is supplied to the respective input of the discriminator 41. A flip-flop circuit FF connected with its input to the clock signal generator 16 is connected to a logic circuit arrangement comprising two monoflop circuits MF2 and MF3 as well as five NAND-gates and a NOR-gate at the output of which the signal T2n /T2n+1 is provided for the time gating of the discriminator circuit 42. The flip-flop circuit FF is a bi-stable multi-vibrator while the monoflop circuits MF1, MF2, and MF3 are mono-stable multi-vibrators. The time constants of the three mono-stable multi-vibrators are independent of one another and are adjusted to the respective measuring requirements.
Although the invention has been described with reference to specific example embodiments, it will be appreciated, that it is intended to cover all modifications and equivalents within the scope of the appended claims.
|Patente citada||Fecha de presentación||Fecha de publicación||Solicitante||Título|
|US3752582 *||27 Ene 1971||14 Ago 1973||Bendix Corp||Optical range and range-rate sensor|
|US4068952 *||23 Jul 1976||17 Ene 1978||Hughes Aircraft Company||Range testing system having simulated optical targets|
|US4521107 *||26 Sep 1984||4 Jun 1985||Mitec Moderne Industrietechnik Gmbh||Apparatus for measuring distances by measuring time of travel of a measuring light pulse|
|EP0057447A1 *||29 Ene 1982||11 Ago 1982||MTC Messtechnik und Optoelektronik AG||Distance measuring apparatus according to the principles of the travel time measurement of a light pulse|
|Patente citante||Fecha de presentación||Fecha de publicación||Solicitante||Título|
|US4888477 *||3 Nov 1988||19 Dic 1989||Ford Aerospace Corporation||Range measurement for active optical recognition devices|
|US4938590 *||10 Ago 1988||3 Jul 1990||Nitto Machinery Co., Ltd.||Liquid level indicator using laser beam|
|US5054911 *||20 Dic 1989||8 Oct 1991||Kabushiki Kaisha Topcon||Light wave distance measuring instrument of the pulse type|
|US5202742 *||3 Oct 1990||13 Abr 1993||Aisin Seiki Kabushiki Kaisha||Laser radar for a vehicle lateral guidance system|
|US5243553 *||2 Jul 1991||7 Sep 1993||Loral Vought Systems Corporation||Gate array pulse capture device|
|US5262837 *||21 Oct 1992||16 Nov 1993||Norm Pacific Automation Corp.||Laser range finder|
|US5293162 *||9 Mar 1992||8 Mar 1994||Bachalo William D||Laser based tracking device for detecting the distance between a vehicle and a roadway marker|
|US5317375 *||25 Feb 1992||31 May 1994||Stanley Electric Co., Ltd.||Optical distance measuring apparatus|
|US5357331 *||24 Mar 1993||18 Oct 1994||Flockencier Stuart W||System for processing reflected energy signals|
|US5357432 *||24 Nov 1993||18 Oct 1994||Aisin Seiki Kabushiki Kaisha||Automatic lateral guidance control system|
|US5390118 *||24 Nov 1993||14 Feb 1995||Aisin Seiki Kabushiki Kaisha||Automatic lateral guidance control system|
|US5430537 *||3 Sep 1993||4 Jul 1995||Dynamics Research Corporation||Light beam distance encoder|
|US5442360 *||28 Abr 1992||15 Ago 1995||Alcatel N.V.||Echo distance-measuring system with calibration apparatus|
|US5510890 *||18 Oct 1993||23 Abr 1996||Gec-Marconi Limited||Laser radar with reference beam storage|
|US5530539 *||10 Feb 1994||25 Jun 1996||Erwin Sick Gmbh, Optik-Elektronik||Apparatus for measuring the transit time of electromagnetic waves|
|US5574552 *||19 Ene 1995||12 Nov 1996||Laser Technology, Inc.||Self-calibrating precision timing circuit and method for a laser range finder|
|US5612779 *||19 Ene 1995||18 Mar 1997||Laser Technology, Inc.||Automatic noise threshold determining circuit and method for a laser range finder|
|US5652651 *||19 Ene 1995||29 Jul 1997||Laser Technology, Inc.||Laser range finder having selectable target acquisition characteristics and range measuring precision|
|US5703678 *||23 Sep 1996||30 Dic 1997||Laser Technology, Inc.||Self-calibrating precision timing circuit and method for a laser range finder|
|US5825464 *||3 Ene 1997||20 Oct 1998||Lockheed Corp||Calibration system and method for lidar systems|
|US5880821 *||26 Ago 1997||9 Mar 1999||Laser Technology, Inc.||Self-calibrating precision timing circuit and method for a laser range finder|
|US5946081 *||8 Dic 1997||31 Ago 1999||Asia Optical Co., Inc.||Method and apparatus for reducing the noise in the receiver of a laser range finder|
|US5953109 *||8 Dic 1997||14 Sep 1999||Asia Optical Co., Inc.||Method and apparatus for improving the accuracy of laser range finding|
|US6057910 *||21 Ene 1999||2 May 2000||Laser Technology, Inc.||Self-calibrating precision timing circuit and method for a laser range finder|
|US6115113 *||2 Dic 1998||5 Sep 2000||Lockheed Martin Corporation||Method for increasing single-pulse range resolution|
|US6226077||25 Feb 2000||1 May 2001||Laser Technology, Inc.||Self-calibrating precision timing circuit and method for a laser range finder|
|US6445444||26 Ene 2001||3 Sep 2002||Laser Technology, Inc.||Self-calibrating precision timing circuit and method for a laser range finder|
|US6512574||12 Feb 2001||28 Ene 2003||Asia Optical Co., Inc.||Light receiving circuit of laser range finder|
|US6917415 *||30 Oct 2002||12 Jul 2005||Hilti Aktiengesellschaft||Method of and apparatus for electro-optical distance measurement|
|US6965438 *||11 Dic 2002||15 Nov 2005||Lg Industrial Systems Co., Ltd.||Vehicle measuring apparatus and method for toll collection system|
|US7030807 *||10 Mar 2005||18 Abr 2006||Fujitsu Limited||Radar device|
|US7053992||4 Mar 2004||30 May 2006||Meade Instruments Corporation||Rangefinder and method for collecting calibration data|
|US7359039 *||2 Dic 2005||15 Abr 2008||Mariusz Kloza||Device for precise distance measurement|
|US7414707||3 May 2006||19 Ago 2008||Meade Instruments Corporation||Rangefinder and method for collecting calibration data|
|US7508497||23 Nov 2004||24 Mar 2009||Meade Instruments Corporation||Rangefinder with reduced noise receiver|
|US7684017||26 Oct 2007||23 Mar 2010||Callaway Golf Company||Laser range finder for use on a golf course|
|US7844183 *||22 Jun 2006||30 Nov 2010||Saab Ab||System and a method for transmission of information|
|US8279417||17 Mar 2010||2 Oct 2012||Callaway Golf Company||Laser range finder for use on a golf course|
|US8451433||6 Ago 2008||28 May 2013||Qinetiq Limited||Range-finding method and apparatus|
|US8781780||25 Dic 2009||15 Jul 2014||Kabushiki Kaisha Topcon||Electro-optical distance measuring method and electro-optical distance measuring device|
|US8836955 *||22 Ago 2009||16 Sep 2014||Carl Zeiss Ag||Device and method for measuring a surface|
|US20040008514 *||11 Dic 2002||15 Ene 2004||Sang-Jean Lee||Vehicle measuring apparatus and method for toll collection system|
|US20040085526 *||30 Oct 2002||6 May 2004||Torsten Gogolla||Method of and apparatus for electro-optical distance measurement|
|US20050110976 *||23 Nov 2004||26 May 2005||Labelle John||Rangefinder with reduced noise receiver|
|US20050110977 *||4 Mar 2004||26 May 2005||Labelle John||Rangefinder and method for collecting calibration data|
|US20050174281 *||10 Mar 2005||11 Ago 2005||Kaoru Yokoo||Radar device|
|US20060215149 *||3 May 2006||28 Sep 2006||Labelle John||Rangefinder and method for collecting calibration data|
|US20070024841 *||2 Dic 2005||1 Feb 2007||Mariusz Kloza||Device for precise distance measurement|
|US20100177298 *||17 Mar 2010||15 Jul 2010||Callaway Golf Company||laser range finder for use on a golf course|
|US20100261145 *||22 Jun 2006||14 Oct 2010||Saab Ab||A system and a method for transmission of information|
|US20100265491 *||6 Ago 2008||21 Oct 2010||Qinetiq Limited||Range-finding method and apparatus|
|US20110176146 *||22 Ago 2009||21 Jul 2011||Cristina Alvarez Diez||Device and method for measuring a surface|
|CN102854510A *||16 Ago 2012||2 Ene 2013||苏州启智机电技术有限公司||High precision laser range finder|
|DE10014125A1 *||22 Mar 2000||27 Sep 2001||Adc Automotive Dist Control||Optical system performs at least one reference measurement as transition time measurement for optical signal in two reference light conductors to determine distance measurement correction|
|DE10044690B4 *||4 Jul 2000||11 May 2006||Eads Deutschland Gmbh||Verfahren und Vorrichtung zur Messung von Entfernungen und/oder Geschwindigkeiten durch Laserpulse|
|EP1251363A2 *||6 Mar 2002||23 Oct 2002||KROHNE MESSTECHNIK GMBH & CO. KG||Processing method for a frequency signal|
|EP1251363A3 *||6 Mar 2002||9 Jun 2004||KROHNE MESSTECHNIK GMBH & CO. KG||Processing method for a frequency signal|
|EP3072162A4 *||21 Nov 2014||5 Jul 2017||Ottomotto Llc||Lidar scanner calibration|
|WO1991013319A1 *||26 Abr 1990||5 Sep 1991||International Measurement, Inc.||Laser detector system|
|WO1996022509A1 *||29 Nov 1995||25 Jul 1996||Laser Technology, Inc.||Laser range finder|
|Clasificación de EE.UU.||356/5.07|
|Clasificación internacional||G01S7/483, G01S7/481, G01S17/10|
|Clasificación cooperativa||G01S7/483, G01S7/4818, G01S17/105|
|Clasificación europea||G01S17/10C, G01S7/483|
|22 Abr 1988||AS||Assignment|
Owner name: MESSERSCHMITT-BOELKOW-BLOHM GESELLSCHAFT MIT BESCH
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNORS:MANHART, SIGMUND;DYRNA, PETER;KUNKEL, BERND;REEL/FRAME:004850/0961
Effective date: 19861107
Owner name: MESSERSCHMITT-BOELKOW-BLOHM GESELLSCHAFT MIT BESCH
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MANHART, SIGMUND;DYRNA, PETER;KUNKEL, BERND;REEL/FRAME:004850/0961
Effective date: 19861107
|24 Feb 1992||FPAY||Fee payment|
Year of fee payment: 4
|23 Feb 1996||FPAY||Fee payment|
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|22 Feb 2000||FPAY||Fee payment|
Year of fee payment: 12